Certain luminaires are designed for illuminating stacked material along warehouse aisles or the like. An example of such a luminaire is disclosed and claimed in U.S. Pat. No. 4,303,971 - Hogue et al, assigned to the assignee of the present invention. These luminaires are typically disposed above the aisle in spaced locations along the aisle length. In the usual installation of this type, each luminaire directs light toward the stacked material at the edges of the aisle, with a major portion of the luminous flux being directed to the areas midway between adjacent luminaires. Traditionally, luminaires used in these applications have produced intense illumination on the stacks immediately adjacent the luminaire, leaving the upper areas of the stacks between the luminaires relatively dark and difficult to see. To alleviate this problem, luminaires have some times been Provided with "up-light" openings in the top of their reflectors. But even these luminaires do not provide an effective solution to this problem, since most of the light that is emitted upwardly is directed toward the ceiling only.